Lateralization of connexin43 (Cx43) in the myocyte in pathologic cardiac conditions such as hypertrophy, ischemia and infarction, in some instances accompanied by a generalized down-regulation of Cx43 expression, is a process termed structural gap junction remodeling (GJR). The contribution of GJR to the arrhythmic substrate is well-established in both human disease states and in animal models. However, a detailed characterization of GJR in a mouse model that can be used for the study of the underlying molecular mechanisms has not yet been described. We hypothesize that structural GJR in cardiac disease, causing altered electrophysiology in the heart and facilitating arrhythmias, results from a defect in trafficking of connexin protein from non-junctional locations on the plasma membrane to the gap junction plaque. To test this hypothesis, we have developed a novel murine pacing model of GJR, with which we will characterize the time course of altered Cx43 expression with pacing, as well as the reversibility of the remodeling process after cessation of pacing. Our preliminary experiments indicate that we can reproducibly induce structural GJR in the mouse heart by ventricular pacing for six hours at rates just above those of sinus rhythm. In addition to studying the development of GJR with short-term pacing, we will investigate how pacing-induced GJR affects the interaction of Cx43 with known binding partners and other intercalated disc proteins and whether the sub-cellular localization of these associated proteins is altered in GJR. We will study the effect of pacing-induced structural GJR on cardiac electrophysiology and function. We will use genetic and biochemical approaches to examine whether structural GJR results in the increased deposition of full gap junctions or connexon subunits at the lateral borders of cardiac myocytes. Lastly, we will investigate Cx43 trafficking in GJR using a "tet-on" inducible system for in vivo expression of a myc-tagged Cx43 construct. These studies are intended to investigate mechanisms underlying structural GJR in a novel murine model which allows for the use of genetic manipulation that is not feasible with other approaches. Through these studies, we hope to shed light on the pathways involved in GJR and uncover potential therapeutic targets to prevent or reverse this highly arrhythmogenic process.